1. Field of the Invention
This invention relates to an optical disc assembly in which an audio signal, a video signal, a data processing signal or any other signal is recorded, and in which the signal is reproduced with light such as laser, and a disc drive machine for driving the optical disc.
2. Description of the Prior Art
FIG. 1 and FIG. 3 show conventional optical discs 1 and 2 on which an audio signal or a video signal is recorded to be optically read out. The optical disc 1 of FIG. 1 is single-sided. The optical disc 2 of FIG. 3 is double-sided. FIG. 2 is an enlarged view of a portion of the optical disc 1 of FIG. 1. In FIG. 1 and FIG. 2, a main body is made of transparent material such as glass or plastics which is about 1.1 mm in thickness. A spiral track 3 is formed on one side surface of the main body. Signal indentations 4 are formed with high density in the spiral track 3, which are about 0.2.mu. in depth. They may be formed by a press as a usual record disc. A reflecting film 5 is formed on the spiral track 3 for example by vapor deposition of aluminum. Further, a protecting film 6, such as a plastic film, is formed on the reflecting film 5 in order to protect the signal indentations 4.
When the signal is reproduced from the optical disc 1, the recorded spiral track 3 of the rotating optical disc 1 is transmitted through an objective lens 8 by laser light 7. The signal indentations 4 are optically read out by the reflecting laser light from the reflecting film 5, without any physical contact with the disc.
The two-sided optical disc 2 of FIG. 3 is obtained by attaching two optical discs 1 to each other back to back.
Basically, the conventional optical disc is one-sided. Two optical discs should be attached to each other to obtain a two-sided optical disc. The protecting film 6 is always formed on the recorded spiral track 3 in order to prevent the very fine signal indentation 4 (about 0.2.mu. in depth) from being touched directly by the user, and the recorded spiral track 3 damaged by deposition of dust. Accordingly, the conventional optical disc is inconvenient for mass production and subject to easy damage.